Controlling crop diseases using induced resistance: challenges for the future
TL;DR: Understanding of the impact of environment, genotype, crop nutrition, and other influences on the expression of induced resistance is still poor and further research geared towards incorporating induced resistance into disease management programmes, if appropriate, is required.
Abstract: A number of different types of induced resistance have been defined based on differences in signalling pathways and spectra of effectiveness, including systemic acquired resistance and induced systemic resistance. Such resistance can be induced in plants by application of a variety of biotic and abiotic agents. The resulting resistance tends to be broad-spectrum and can be long-lasting, but is rarely complete, with most inducing agents reducing disease by between 20 and 85%. Since induced resistance is a host response, its expression under field conditions is likely to be influenced by a number of factors, including the environment, genotype, crop nutrition and the extent to which plants are already induced. Although research in this area has increased over the last few years, our understanding of the impact of these influences on the expression of induced resistance is still poor. There have also been a number of studies in recent years aimed at understanding of how best to use induced resistance in practical crop protection. However, such studies are relatively rare and further research geared towards incorporating induced resistance into disease management programmes, if appropriate, is required.
Citations
More filters
TL;DR: This review focuses on molecular processes at the interface between plant roots and ISR-eliciting mutualists, and on the progress in the understanding of ISR signaling and systemic defense priming.
Abstract: Beneficial microbes in the microbiome of plant roots improve plant health. Induced systemic resistance (ISR) emerged as an important mechanism by which selected plant growth–promoting bacteria and fungi in the rhizosphere prime the whole plant body for enhanced defense against a broad range of pathogens and insect herbivores. A wide variety of root-associated mutualists, including Pseudomonas, Bacillus, Trichoderma, and mycorrhiza species sensitize the plant immune system for enhanced defense without directly activating costly defenses. This review focuses on molecular processes at the interface between plant roots and ISR-eliciting mutualists, and on the progress in our understanding of ISR signaling and systemic defense priming. The central role of the root-specific transcription factor MYB72 in the onset of ISR and the role of phytohormones and defense regulatory proteins in the expression of ISR in aboveground plant parts are highlighted. Finally, the ecological function of ISR-inducing microbes in the root microbiome is discussed.
1,856 citations
Cites background from "Controlling crop diseases using ind..."
...However, there are many examples of PGPR or PGPF that induce ISR under field conditions when introduced to soil or planting material (64, 175)....
[...]
...Generally, induced resistance confers an enhanced level of protection against a broad spectrum of attackers (175)....
[...]
...Beneficial microbes with ISR-eliciting properties have often been selected from large screens of the root microbiome for members that have biological control activities (37, 64, 136, 175)....
[...]
...Describing the extensive list of ISR-inducing beneficial microbes is beyond the scope of this review, so readers are referred to several excellent review articles for additional information on this topic (2, 20, 37, 46, 62, 64, 118, 136, 154, 158, 159, 175)....
[...]
...Although the importance of the root microbiota in improving nutrient availability, antagonizing soilborne pathogens, promoting plant growth, and priming the plant’s immune system is well established and abundantly used in biocontrol strategies (76, 175), we are still ignorant about how plants are able to shape the composition of the root microbiome to their own benefit....
[...]
TL;DR: To realize the objective of worldwide sustainable agriculture, it is essential that the many mechanisms employed by PGPB first be thoroughly understood thereby allowing workers to fully harness the potentials of these microbes.
Abstract: The idea of eliminating the use of fertilizers which are sometimes environmentally unsafe is slowly becoming a reality because of the emergence of microorganisms that can serve the same purpose or even do better. Depletion of soil nutrients through leaching into the waterways and causing contamination are some of the negative effects of these chemical fertilizers that prompted the need for suitable alternatives. This brings us to the idea of using microbes that can be developed for use as biological fertilizers (biofertilizers). They are environmentally friendly as they are natural living organisms. They increase crop yield and production and, in addition, in developing countries, they are less expensive compared to chemical fertilizers. These biofertilizers are typically called plant growth-promoting bacteria (PGPB). In addition to PGPB, some fungi have also been demonstrated to promote plant growth. Apart from improving crop yields, some biofertilizers also control various plant pathogens. The objective of worldwide sustainable agriculture is much more likely to be achieved through the widespread use of biofertilizers rather than chemically synthesized fertilizers. However, to realize this objective it is essential that the many mechanisms employed by PGPB first be thoroughly understood thereby allowing workers to fully harness the potentials of these microbes. The present state of our knowledge regarding the fundamental mechanisms employed by PGPB is discussed herein.
592 citations
Cites background from "Controlling crop diseases using ind..."
...ISR confers a high level of protection which is controlled by a network of coordinated signaling pathways which are dominated and majorly regulated by plant hormones sharing signaling components (Pieterse et al. 2012, 2014; Walters et al. 2013)....
[...]
TL;DR: Priming is an adaptive strategy that improves the defensive capacity of plants and can be durable and maintained throughout the plant's life cycle and can even be transmitted to subsequent generations, therefore representing a type of plant immunological memory.
Abstract: Priming is an adaptive strategy that improves the defensive capacity of plants. This phenomenon is marked by an enhanced activation of induced defense mechanisms. Stimuli from pathogens, beneficial microbes, or arthropods, as well as chemicals and abiotic cues, can trigger the establishment of priming by acting as warning signals. Upon stimulus perception, changes may occur in the plant at the physiological, transcriptional, metabolic, and epigenetic levels. This phase is called the priming phase. Upon subsequent challenge, the plant effectively mounts a faster and/or stronger defense response that defines the postchallenge primed state and results in increased resistance and/or stress tolerance. Priming can be durable and maintained throughout the plant's life cycle and can even be transmitted to subsequent generations, therefore representing a type of plant immunological memory.
537 citations
Cites background from "Controlling crop diseases using ind..."
...CONCLUSIONS Priming is an effective strategy to combat biotic and abiotic stresses, and it therefore represents a potential approach to enhance plant protection in agricultural systems (138)....
[...]
...There has already been a considerable translation of knowledge from the laboratory to the field (31, 138)....
[...]
...Transgenerational Resistance in Crops Since the discovery that defense priming can be transmitted to subsequent generations, several publications have described similar findings in crops (138)....
[...]
TL;DR: A historical overview of the progress made in elucidating the role of SA in signaling plant immune responses is presented and how crosstalk among the different hormone signaling pathways leads to an immune response that is both robust and optimized for maximal efficacy, depending on the identity of the attacking pathogen is clarified.
Abstract: This article is part of the Distinguished Review Article Series in Conceptual and Methodological Breakthroughs in Molecular Plant-Microbe Interactions. Salicylic acid (SA) is a critical plant hormone that regulates numerous aspects of plant growth and development as well as the activation of defenses against biotic and abiotic stress. Here, we present a historical overview of the progress that has been made to date in elucidating the role of SA in signaling plant immune responses. The ability of plants to develop acquired immunity after pathogen infection was first proposed in 1933. However, most of our knowledge about plant immune signaling was generated over the last three decades, following the discovery that SA is an endogenous defense signal. During this timeframe, researchers have identified i) two pathways through which SA can be synthesized, ii) numerous proteins that regulate SA synthesis and metabolism, and iii) some of the signaling components that function downstream of SA, including a large number of SA targets or receptors. In addition, it has become increasingly evident that SA does not signal immune responses by itself but, rather, as part of an intricate network that involves many other plant hormones. Future efforts to develop a comprehensive understanding of SA-mediated immune signaling will therefore need to close knowledge gaps that exist within the SA pathway itself as well as clarify how crosstalk among the different hormone signaling pathways leads to an immune response that is both robust and optimized for maximal efficacy, depending on the identity of the attacking pathogen.
292 citations
Cites background from "Controlling crop diseases using ind..."
...T he f in al p ub lis he d ve rs io n m ay d if fe r. 35 variable, with disease reduction ranging from 20-85% (Walters et al., 2013)....
[...]
...Several synthetic compounds that induce SAR to a similar range of pathogens as SA have been identified, including INA, BTH, PBZ and PBZ’s active metabolite 1,2-benzisothiazol-3(2H)-one 1,1-dioxide (BIT; Gozzo and Faoro, 2013; Walters et al., 2013; Conrath et al., 2015)....
[...]
...…inducing defenses, ii) variable levels of efficacy, depending on the plant cultivar and dosage, and iii) the possibility that activating SA-induced defenses will suppress JA signaling, and thereby enhance crop susceptibility to necrotrophic pathogens (Gozzo and Faoro, 2013; Walters et al., 2013)....
[...]
TL;DR: This review summarizes recent achievements and knowledge of the elicitation of host defenses to control postharvest decay of fruit and vegetables, and provides an outlook on the new challenges in this fascinating subject.
274 citations
References
More filters
TL;DR: A conceptual model of the evolution of plant defense is concluded, in which plant physioligical trade-offs interact with the abiotic environment, competition and herbivory.
Abstract: Physiological and ecological constraints play key roles in the evolution of plant growth patterns, especially in relation to defenses against herbivores. Phenotypic and life history theories are unified within the growth-differentiation balance (GDB) framework, forming an integrated system of theories explaining and predicting patterns of plant defense and competitive interactions in ecological and evolutionary time. Plant activity at the cellular level can be classified as growth (cell division and enlargement) of differentiation (chemical and morphological changes leading to cell maturation and specialization). The GDB hypothesis of plant defense is premised upon a physiological trade-off between growth and differentiation processes. The trade-off between growth and defense exists because secondary metabolism and structural reinforcement are physiologically constrained in dividing and enlarging cells, and because they divert resources from the production of new leaf area. Hence the dilemma of plants: Th...
3,843 citations
TL;DR: In this article, a pot trial was carried out to investigate the effect of biochar produced from greenwaste by pyrolysis on the yield of radish and the soil quality of an Alfisol.
Abstract: A pot trial was carried out to investigate the effect of biochar produced from greenwaste by pyrolysis on the yield of radish (Raphanus sativus var. Long Scarlet) and the soil quality of an Alfisol. Three rates of biochar (10, 50 and 100 t/ha) with and without additional nitrogen application (100 kg N/ha) were investigated. The soil used in the pot trial was a hardsetting Alfisol (Chromosol) (0–0.1 m) with a long history of cropping. In the absence of N fertiliser, application of biochar to the soil did not increase radish yield even at the highest rate of 100 t/ha. However, a significant biochar × nitrogen fertiliser interaction was observed, in that higher yield increases were observed with increasing rates of biochar application in the presence of N fertiliser, highlighting the role of biochar in improving N fertiliser use efficiency of the plant. For example, additional increase in DM of radish in the presence of N fertiliser varied from 95% in the nil biochar control to 266% in the 100 t/ha biochar-amended soils. A slight but significant reduction in dry matter production of radish was observed when biochar was applied at 10 t/ha but the cause is unclear and requires further investigation. Significant changes in soil quality including increases in pH, organic carbon, and exchangeable cations as well as reduction in tensile strength were observed at higher rates of biochar application (>50 t/ha). Particularly interesting are the improvements in soil physical properties of this hardsetting soil in terms of reduction in tensile strength and increases in field capacity.
1,682 citations
"Controlling crop diseases using ind..." refers background in this paper
...Amendment of soil with biochar has been reported to improve crop performance by, for example, increasing nutrient retention (Chan et al., 2007), promoting mycorrhizal fungi in soil (Warnock et al....
[...]
TL;DR: This review aims to characterize the interaction between biotic and abiotic stress responses at a molecular level, focusing on regulatory mechanisms important to both pathways.
Abstract: Plant responses to different stresses are highly complex and involve changes at the transcriptome, cellular, and physiological levels. Recent evidence shows that plants respond to multiple stresses differently from how they do to individual stresses, activating a specific programme of gene expression relating to the exact environmental conditions encountered. Rather than being additive, the presence of an abiotic stress can have the effect of reducing or enhancing susceptibility to a biotic pest or pathogen, and vice versa. This interaction between biotic and abiotic stresses is orchestrated by hormone signalling pathways that may induce or antagonize one another, in particular that of abscisic acid. Specificity in multiple stress responses is further controlled by a range of molecular mechanisms that act together in a complex regulatory network. Transcription factors, kinase cascades, and reactive oxygen species are key components of this cross-talk, as are heat shock factors and small RNAs. This review aims to characterize the interaction between biotic and abiotic stress responses at a molecular level, focusing on regulatory mechanisms important to both pathways. Identifying master regulators that connect both biotic and abiotic stress response pathways is fundamental in providing opportunities for developing broad-spectrum stress-tolerant crop plants.
1,471 citations
"Controlling crop diseases using ind..." refers background in this paper
...Under field conditions, plants are exposed to multiple environmental challenges simultaneously (Atkinson and Urwin, 2012)....
[...]
...Interactions can also occur between abiotic stress and resistance to pathogens (Ayres, 1984; Atkinson and Urwin, 2012)....
[...]
TL;DR: The potential of Piriformospora indica to induce resistance to fungal diseases and tolerance to salt stress in the monocotyledonous plant barley is reported on.
Abstract: Disease resistance strategies are powerful approaches to sustainable agriculture because they reduce chemical input into the environment. Recently, Piriformospora indica, a plant-root-colonizing basidiomycete fungus, has been discovered in the Indian Thar desert and was shown to provide strong growth-promoting activity during its symbiosis with a broad spectrum of plants [Verma, S. et al. (1998) Mycologia 90, 896-903]. Here, we report on the potential of P. indica to induce resistance to fungal diseases and tolerance to salt stress in the monocotyledonous plant barley. The beneficial effect on the defense status is detected in distal leaves, demonstrating a systemic induction of resistance by a root-endophytic fungus. The systemically altered “defense readiness” is associated with an elevated antioxidative capacity due to an activation of the glutathione-ascorbate cycle and results in an overall increase in grain yield. Because P. indica can be easily propagated in the absence of a host plant, we conclude that the fungus could be exploited to increase disease resistance and yield in crop plants.
1,197 citations
"Controlling crop diseases using ind..." refers background in this paper
...Fungal and bacterial endophytes have been shown to induce resistance (Waller et al., 2005; Kang et al., 2007), and resistance can also be induced by avirulent nematode species (Ogallo and McClure, 1996; Kosaka et al....
[...]
...Root colonization by the endophytic basidiomycete fungus Piriformospora indica protects various plant species against abiotic and biotic stresses (Waller et al., 2005; Stein et al., 2008)....
[...]
TL;DR: In this paper, the authors focus on biochar effects on mycorrhizal associations, and examine hypotheses pertaining to four mechanisms by which biochar could influence mycRH abundance and/or functioning.
Abstract: Experiments suggest that biomass-derived black carbon (biochar) affects microbial populations and soil biogeochemistry. Both biochar and mycor- rhizal associations, ubiquitous symbioses in terrestrial ecosystems, are potentially important in various ecosystem services provided by soils, contributing to sustainable plant production, ecosystem restoration, and soil carbon sequestration and hence mitigation of global climate change. As both biochar and mycor- rhizal associations are subject to management, under- standing and exploiting interactions between them could be advantageous. Here we focus on biochar effects on mycorrhizal associations. After reviewing the experimental evidence for such effects, we critically examine hypotheses pertaining to four mechanisms by which biochar could influence mycorrhizal abundance and/or functioning. These mechanisms are (in decreas- ing order of currently available evidence supporting them): (a) alteration of soil physico-chemical proper- ties; (b) indirect effects on mycorrhizae through effects on other soil microbes; (c) plant-fungus signaling interference and detoxification of allelochemicals on biochar; and (d) provision of refugia from fungal grazers. We provide a roadmap for research aimed at testing these mechanistic hypotheses.
1,093 citations
"Controlling crop diseases using ind..." refers background in this paper
..., 2007), promoting mycorrhizal fungi in soil (Warnock et al., 2007) and altering soil microbial populations and functions (Steiner et al....
[...]